Latency reduction is one of the well recognized work items in GSM/EDGE Release 7 radio access network (GERAN) evolution. There are primarily two techniques being worked on in this area; namely the reduced transmission time interval (RTTI) feature and the fast positive acknowledgement/negative acknowledgement (ACK/NACK) reporting (FANR) feature.
Both the RTTI feature and the FANR feature can either work separately, or in conjunction with each other. Furthermore, both the RTTI feature and the FANR feature can be used in conjunction with evolved general packet radio services (EGPRS) modulation and coding schemes MCS-1 to MCS-9 (except for MCS-4 and MCS-9 where FANR cannot be implemented) or with the novel Release 7 and beyond EGPRS-2 modulation and coding schemes DAS-5 to DAS-12, DBS-5 to DBS-12, UAS-7 to UAS-11 and UBS-5 to UBS-12. RTTI mode of operation and FANR mode of operation are also possible with other existing Release 7 GERAN evolution features, such as the Downlink Dual-Carrier (DLDC) feature or Downlink Advanced Receiver Performance (DARP) operation.
In the prior art described by pre-Release 7 global system for mobile communication (GSM), general packet radio services (GPRS) and EGPRS modes of operation, an ACK/NACK report was typically sent in explicit radio link control (RLC)/medium access control (MAC) protocol messages, also referred to as RLC/MAC control blocks. Examples for such explicit RLC/MAC protocol messages include Packet Downlink (DL) ACK/NACK or Packet Uplink (UL) ACK/NACK messages. The RLC/MAC control block is addressed to a certain radio resource, called a temporary block flow (TBF).
A TBF is a temporal connection between a mobile station and a network to support a uni-directional transfer of data. If supported by the mobile station and the network, more than one (1) TBF can be allocated to a mobile station. A TBF is temporary and maintained only for the duration of the data transfer. Each TBF is assigned a temporary flow identity (TFI) by the network. The TFI is unique among concurrent TBFs in each direction and is used instead of mobile station identity in the RLC/MAC layer. For example, in GPRS and EGPRS modes of operation, the same TFI is included in every RLC/MAC header belonging to a particular TBF in order to allow the intended receiver, (i.e., the wireless transmit/receive unit (WTRU) or network), to determine the addressee of a received radio block.
In order to reduce transmission latencies associated with the use of an entire RLC/MAC control block, it has been proposed in GSM/(E)GPRS Release 7 to send the ACK/NACK report for a certain TBF “piggybacked” onto an RLC/MAC data block by puncturing a number of bits from the channel-coded data portion of the radio block at no loss of data. This new field is inserted, when needed, into the RLC/MAC data block and carries the ACK/NACK report as part of the radio block referred to as a piggybacked ACK/NACK (PAN) field. The insertion of PAN is possible, and can be configured, both for the DL and UL directions. The PAN field, when sent to a WTRU in the DL, carries ACKs or NACKs for data units or protocol data units (PDUs) previously sent by the WTRU in the UL direction, and vice versa. The presence or absence of the PAN field in a radio block is indicated by the RLC/MAC header, either by a bit or bit field setting, or by setting other code points depending on the RLC/MAC header type accordingly, and therefore depends on the EGPRS/EGPRS-2 modulation and coding scheme chosen for the transmission of the radio block. In the DL direction, the PAN field of an RLC/MAC data block can possibly be addressed to a WTRU that is not the intended receiver of the data units (or PDUs) in the radio block. Alternatively, the PAN field and the data units (or PDUs) of the radio block can be intended for the same WTRU. Both for DL and UL directions, the TBF to which the PAN field refers can possibly be different from the TBF corresponding to the data units (or PDUs) of the radio block, even if the receiver is the same physical unit (WTRU, or network).
The actual bit field(s) carrying the ACKs or NACKs in the PAN field can be encoded according to different procedures, for example using a starting sequence number (SSN)-based approach or a time-based approach.
Since the PAN field is included in a data block that may be addressed to a different TBF, it is necessary to identify to which TBF the PAN field is addressed. In addition, a need for additional methods for PAN transmission and reception modes arises from additional operation scenarios in GSM/(E)GPRS networks. For example, identification of the TBF to which the PAN is addressed should also be possible in the case of multiple TBFs assigned to one (1) receiver, such as one WTRU. This mode of operation is needed to facilitate multiple TBFs mode of operation with FANR.
PAN transmissions may be made for special cases, such as when a PAN field not actually addressed to a TBF is sent. This mode of operation is needed to facilitate transmission and reception of a PAN field not pertaining to data units (or PDUs) and their associated TFI(s). PAN transmissions may also be made where a PAN is to be addressed and to be reliably decoded by more than one receiver. For example, this mode of operation is needed when the PAN is sent to a group of receivers. Therefore, methods are sought after that allow for such modes of operation.